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Abstract:

There is provided a heat exchanger element and a heat exchanger which are
smaller, lighter in weight, and lower in cost than conventional heat
exchange bodies, heat exchangers and the like. In the honeycomb
structure, t≧0.2, ρ>100,
20≦t×ρ≦250, and 10,000≦λ×ρ
are satisfied when thermal conductivity of a material for the partition
walls is taken as λ [W/K˜m], and, regarding a cell structure
of the honeycomb structure, a wall thickness of the partition walls is
taken as t [mm], and a cell density is taken as ρ [cells/sq.in.].

Claims:

1. A heat exchanger element formed as a honeycomb structure having a
plurality of cells partitioned by ceramic partition walls, passing
through in an axial direction from one end face to the other end face,
and functioning as a first fluid passage portion where a heating body as
the first fluid passes; wherein at least one of the partition walls and
an outer peripheral wall of the honeycomb structure is made dense to
avoid the first fluid passing through the first fluid passage portion and
a second fluid receiving heat from the first fluid by passing along an
outer peripheral face of the outer peripheral wall of the honeycomb
structure from being mixed together, and all of t≧0.2,
ρ>100, 20.ltoreq.t×ρ≦250, and
10,000.ltoreq.λ×ρ are satisfied when thermal conductivity
of a material for the partition walls of the honeycomb structure is taken
as λ [W/Km], and, in a cell structure of the honeycomb structure, a
wall thickness of the partition walls is taken as t [mm] and a cell
density is taken as ρ [cells/sq.in.].

2. The heat exchanger element according to claim 1, wherein
20.ltoreq.O≦60 and 1.66.ltoreq.L/O<7.5 are satisfied when, in
the cell structure of the honeycomb structure, a circle-equivalent
diameter of a cross-sectional area of a cross section perpendicular to
the axial direction of the honeycomb structure is taken as O [mm], and
the entire length in the axial direction of the honeycomb structure is
taken as L [mm].

3. A heat exchanger provided with the honeycomb structure as the heat
exchanger element according to claim 1 and a casing having an inlet port
and an outlet port for the second fluid and containing the honeycomb
structure therein, wherein an inside of the casing functions as the
second fluid passage portion, and the second fluid receives heat from the
first fluid by passing along the outer peripheral face of the honeycomb
structure in the second fluid passage portion.

4. A heat exchanger provided with the honeycomb structure as the heat
exchanger element according to claim 2 and a casing having an inlet port
and an outlet port for the second fluid and containing the honeycomb
structure therein, wherein an inside of the casing functions as the
second fluid passage portion, and the second fluid receives heat from the
first fluid by passing along the outer peripheral face of the honeycomb
structure in the second fluid passage portion.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a heat exchanger element for
transferring heat of the first fluid (high temperature side) to the
second fluid (low temperature side) and a heat exchanger.

BACKGROUND ART

[0002] There is demanded a technique for heat recovery from high
temperature gas such as combustion exhaust gas of an engine or the like.
As a gas/liquid heat exchanger, fin-provided tube type heat exchangers of
an automobile radiator and an air-conditioning outdoor unit are general.
However, for recovering heat from gas such as automobile exhaust gas, it
is difficult to use a common metallic heat exchanger at high temperature
because of poor thermal resistance. Therefore, heat resistant metal and
ceramic material, and the like having thermal resistance, thermal shock
resistance, corrosion resistance, and so on are suitable. Though a heat
exchanger made of heat resistant metal is known, heat resistant metal has
problems of difficulty in machining, high density and high weight, and
low thermal conduction in addition to high price.

[0003] In the Patent Document 1, there is disclosed a ceramic heat
exchange body, wherein a heating body passage is disposed from one end
face to the other end face of a ceramic main body, and wherein a passage
for a body to be heated is formed between the heating body passages, and
extending in the direction perpendicular to the heating body passages.

[0004] In the Patent Document 2, there is disclosed a ceramic heat
exchanger, wherein a plurality of ceramic heat exchange bodies each
having a heating fluid passage and a non-heating fluid passage formed
therein are disposed in a casing with an unfired ceramic string-shaped
seal material laid between the corresponding faces to be bonded together
of the heat exchange bodies.

[0005] However, since the Patent Documents 1 and 2 have poor productivity
because of a large number of steps such as plugging and slit-forming, the
costs are high. In addition, since the passages of gas/liquid are
disposed in every other row, the piping structure and seal structure of
the fluid become complicated. Further, since a coefficient of heat
transfer of liquid is generally 10 to 100 times larger than that of gas,
the heat transfer area on the gas side is insufficient in these
techniques, and the heat exchanger becomes large in proportion to the
heat transfer area of the gas which limits the heat exchanger
performance.

[0006] In the Patent Documents 3 and 4, since it is necessary that a
honeycomb structural portion and a tube portion are bonded together after
separately producing them, and the productivity is not good, the costs
tend to be high.

PRIOR ART DOCUMENTS

Patent Documents

[0007] Patent Document 1: JP-A-S61-24997 bulletin

[0008] Patent Document
2: JP-B-S63-60319 bulletin

[0009] Patent Document 3: JP-A-S61-83897
bulletin

[0010] Patent Document 4: JP-A-H02-150691 bulletin

SUMMARY OF THE INVENTION

[0011] An object of the present invention is to provide a heat exchanger
element and a heat exchanger which realize downsizing, weight saving, and
cost reduction in comparison with a conventional heat exchange body, heat
exchanger, and the like.

[0012] The present inventors have found out that the aforementioned object
can be solved by specifying the relation between the size and the
coefficient of thermal conductivity of a honeycomb structure functioning
as a heat exchanger element in the case of heat exchange by putting a
heat exchanger element formed as a honeycomb structure in a casing,
passing the first fluid through the cells of the honeycomb structure, and
passing the second fluid along the outer peripheral face of the honeycomb
structure in the casing. That is, according to the present invention,
there are provided the following honeycomb-structured heat exchanger
element and heat exchanger having high temperature efficiency, small
volume of the honeycomb portion, and small pressure drop of the first
fluid.

[0013] [1] A heat exchanger element formed as a honeycomb structure having
a plurality of cells partitioned by ceramic partition walls, passing
through in an axial direction from one end face to the other end face,
and functioning as a first fluid passage portion where a heating body as
the first fluid passes; wherein at least one of the partition walls and
an outer peripheral wall of the honeycomb structure is made so dense that
the first fluid passing through the first fluid passage portion, and the
second fluid receiving heat from the first fluid by passing along an
outer peripheral face of the outer peripheral wall of the honeycomb
structure are not mixed together, and wherein all of t≧0.2,
ρ>100, 20≦t×ρ≦250, and
10,000≦λ×ρ are satisfied when thermal conductivity
of a material for the partition walls of the honeycomb structure is taken
as λ[W/Km], and, a wall thickness of the partition walls is taken
as t [mm] and a cell density is taken as ρ [cells/sq.in.] in a cell
structure of the honeycomb structure.

[0014] [2] The heat exchanger element according to the aforementioned [1],
wherein 20≦O≦60 and 1.66≦L/O≦7.5 are
satisfied when, a circle-equivalent diameter of a cross-sectional area of
a cross section perpendicular to the axial direction of the honeycomb
structure is taken as O [mm], and the entire length in the axial
direction of the honeycomb structure is taken as L [mm] in the cell
structure of the honeycomb structure.

[0015] [3] A heat exchanger provided with the honeycomb structure as the
heat exchanger element according to the aforementioned [1] or [2] and a
casing having an inlet port and an outlet port for the second fluid and
containing the honeycomb structure therein, wherein an inside of the
casing functions as the second fluid passage portion, and the second
fluid receives heat from the first fluid by passing along the outer
peripheral face of the honeycomb structure in the second fluid passage
portion.

[0016] A heat exchanger element and a heat exchanger of the present
invention have a structure which is not complicated and can realize
downsizing, weight saving, and cost reduction in comparison with a
conventional heat exchange body (heat exchanger or its device). In
addition, they have equivalent or better temperature efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1A is a perspective view showing a heat exchanger element
formed as a cylindrical honeycomb structure.

[0018] FIG. 1B is a cross-sectional view cut along a cross section
parallel to the axial direction, showing a heat exchanger element formed
as a cylindrical honeycomb structure.

[0019]FIG. 2A is a perspective view showing a heat exchanger, wherein a
heat exchanger element formed as a cylindrical honeycomb structure is
housed in a casing.

[0020]FIG. 2B is a cross-sectional view cut along a cross section
parallel to the axial direction, showing a heat exchanger, wherein a heat
exchanger element formed as a cylindrical honeycomb structure is housed
in a casing.

[0021]FIG. 2c is a cross-sectional view cut along a cross section
perpendicular to the axial direction, showing a heat exchanger, wherein a
heat exchanger element formed as a cylindrical honeycomb structure is
housed in a casing.

[0022] FIG. 3A is a schematic view showing an embodiment of a heat
exchanger of the present invention, viewed from the first fluid inlet
port side.

[0023]FIG. 3B is a schematic view showing an embodiment of a heat
exchanger of the present invention, where the first fluid and the second
fluid exchange heat by a countercurrent.

[0024]FIG. 4A is a view showing another embodiment of a heat exchanger of
the present invention, where the first fluid and the second fluid
exchange heat by a cross flow, schematically showing an arrangement where
a plurality of honeycomb structures are stacked in layers.

[0025] FIG. 4B is a perspective view showing an embodiment having an
equilateral staggered arrangement of a plurality of honeycomb structures.

[0026] FIG. 4C shows an embodiment having an equilateral staggered
arrangement of a plurality of honeycomb structures viewed from the first
fluid inlet port side.

[0027]FIG. 4D is a view showing an embodiment including honeycomb
structures having different sizes.

[0028]FIG. 5A is a perspective view showing another embodiment of a heat
exchanger, wherein a cylindrical honeycomb structure is housed in a
casing.

[0029]FIG. 5B is a cross-sectional view cut along a cross section
parallel to the axial direction, showing another embodiment of a heat
exchanger, wherein a cylindrical honeycomb structure is housed in a
casing.

[0030]FIG. 5c is a cross-sectional view cut along a cross section
perpendicular to the axial direction, showing another embodiment of a
heat exchanger, wherein a cylindrical honeycomb structure is housed in a
casing.

[0031] FIG. 6 is a cross-sectional view cut along across section parallel
to the axial direction, showing an embodiment of a heat exchanger,
wherein a honeycomb structure provided with a punching metal is housed in
a casing.

[0032] FIG. 7A is a schematic view for explaining the state where the
casing is spirally looped around the honeycomb structure on its outer
peripheral face.

[0033] FIG. 7B is a schematic view in a direction parallel to the axial
direction, for explaining the state where the casing is spirally looped
around the honeycomb structure on its outer peripheral face.

[0034] FIG. 8 is a cross-sectional view cut along a cross section parallel
to the axial direction, showing an embodiment of a heat exchanger,
wherein the casing is provided with a tubular portion and an outside
casing portion as a single unit.

MODE FOR CARRYING OUT THE INVENTION

[0035] Hereinbelow, embodiments of the present invention will be described
with referring to drawings. The present invention is not limited to the
following embodiments, and changes, modifications, and improvements may
be made as long as they do not deviate from the scope of the invention.

[0036] FIG. 1A is a perspective view showing a heat exchanger element of
an embodiment of the present invention. FIG. 1B is a cross-sectional view
cut along a cross section parallel to the axial direction, where the heat
exchanger element is formed as a cylindrical honeycomb structure 1. FIG.
2A shows a perspective view of a heat exchanger 30 where a heat exchanger
element having a cylindrical honeycomb structure 1 is housed in a casing
21, FIG. 2B shows a cross-sectional view cut along a cross section
parallel to the axial direction, and FIG. 2c shows a cross-sectional view
cut along a cross section perpendicular to the axial direction.

[0037] As shown in FIGS. 1A and 1B, the honeycomb structure 1 of the heat
exchanger element is formed into a cylindrical shape. As shown in FIGS.
2A to 2C, the casing 21 of the heat exchanger 30 of the present
embodiment is formed linearly in such a manner that the honeycomb
structure 1, which forms the first fluid passage portion 5 from the first
fluid inlet port 25 to the first fluid outlet port 26, engages with the
casing 21. Also, the second fluid passage portion 6 from the second fluid
inlet port 22 to the second fluid outlet port 23 is formed linearly.
There is given a cross structure where the first fluid passage portion 5
and the second fluid passage portion 6 cross each other. The honeycomb
structure 1 is provided to be engaged with the casing 21. The inlet port
22 and the outlet port 23 of the second fluid are formed oppositely
across the honeycomb structure 1.

[0038] As shown in FIG. 2B, the heat exchanger 30 is provided with the
first fluid passage portion 5 and the second fluid passage portion 6. The
first fluid passage portion 5 is formed of a honeycomb structure 1 having
a plurality of cells 3 partitioned by ceramic partition walls 4, passing
through in the axial direction from one end face 2 to the other end face
2, and allowing the heating body as the first fluid to pass therethrough.
The second fluid passage portion 6 is formed of the casing 21 containing
the honeycomb structure 1 therein, wherein the second fluid inlet port 22
and the second fluid outlet port 23 are formed in the casing 21, and the
second fluid flows over the outer peripheral face 7 of the honeycomb
structure 1 inside the casing 21 to receive heat from the first fluid. In
order to avoid the first fluid and the second fluid from being mixed
together, at least one of the partition walls 4 and the outer peripheral
wall 7h of the honeycomb structure 1 is made dense. Incidentally, "the
second fluid flows over the outer peripheral face 7 of the honeycomb
structure 1" includes both of the case where the second fluid is brought
into direct contact with the outer peripheral face 7 of the honeycomb
structure 1 and the case where the second fluid is not brought into
direct contact with the outer peripheral face 7 of the honeycomb
structure 1.

[0039] The honeycomb structure 1 as a heat exchanger element housed in the
casing 21 has a plurality of cells 3 partitioned by ceramic partition
walls 4, passing through from one end face 2 to the other end face 2, and
allowing a heating body as the first fluid to pass therethrough. The heat
exchanger 30 is configured in such a manner that the first fluid, which
has higher temperature than the second fluid, passes through the cells 3
of the honeycomb structure 1.

[0040] In addition, the second fluid passage portion 6 is formed by the
inner peripheral face 24 of the casing 21 and the outer peripheral face 7
of the honeycomb structure 1. The second fluid passage portion 6 is a
passage portion for the second fluid, which is formed by the casing 21
and the outer peripheral face 7 of the honeycomb structure 1. The second
fluid passage portion 6 is separated from the first fluid passage portion
5 by the partition walls 4 of the honeycomb structure 1 to be able to
conduct heat, receives heat of the first fluid passing through the first
fluid passage portion 5 via the partition walls 4, and transfers heat to
the body to be heated, which is the second fluid passing therethrough.
The first fluid and the second fluid are completely separated from each
other and never mixed together.

[0041] As shown in FIG. 1A, the first fluid passage portion 5 is formed as
a honeycomb structure. In the case of a honeycomb structure, when a fluid
passes through a cell 3, the fluid cannot flow into another cell 3
because of the partition walls 4 and linearly moves from the inlet port
to the outlet port of the honeycomb structure 1. The honeycomb structure
1 in a heat exchanger 30 of the present invention is not plugged, the
heat transfer area of the fluid is increased, and the size of the heat
exchanger can be reduced. This enables to increase the heat transfer
amount per unit volume of the heat exchanger. Further, since it is not
necessary to form plugging portions or to form slits in the honeycomb
structure 1, the heat exchanger 30 enables to reduce production costs.

[0042] In a heat exchanger element of the present invention, when thermal
conductivity of a material for the partition walls 4 of the honeycomb
structure 1 forming the first fluid passage portion 5 is taken as 2
λ [W/Km], and the wall thickness of the partition walls 4 is taken
as t [mm], and the cell density is taken as ρ [cells/sq.in.] in a
cell structure of the honeycomb structure 1; t≧0.2, ρ>100,
20≦t×ρ≦250, and
10,000≦λ×ρ.

[0043] As to t×ρ, 20≦t×ρ≦250, preferably
80≦t×ρ≦250. Such a range of t×ρ enables
to transfer heat of the first fluid effectively to the outer peripheral
wall 7h portion which exchanges heat with the second fluid and to reduce
pressure drop generated by the first fluid while maintaining the
temperature efficiency. As to λ×ρ,
10,000≦λ×ρ, more preferably
20,000≦λ×ρ. Such a range of λ×ρ
enables to efficiently transfer the heat of the first fluid to the outer
peripheral wall 7h portion which exchanges heat with the second fluid
while keeping the pressure drop small.

[0044] O [mm] means a circle-equivalent diameter, which is a diameter of a
circle having the same area as the area of the heat collection portion.
The heat collection portion means the portion collecting heat from the
first fluid, and in case of the honeycomb structure 1, it means the
portion where the cells 3 are formed (excluding the outer peripheral wall
7h). If the honeycomb structure 1 has a cylindrical shape, the diameter
of the portion excluding the outer peripheral wall 7h is O. If a cross
sectional area of cross sections perpendicular to the axial direction of
the honeycomb structure 1 is the same, regardless of the shape of the
honeycomb structure 1, since the average distance from each point of the
heat collection portion to the outer peripheral wall 7h becomes the same,
the heat exchange amount becomes almost the same. Therefore, the
temperature efficiency can be improved by specifying parameters including
the circle-equivalent diameter.

[0045] As to O, 20≦O≦60 is preferable, more preferably
30≦O≦50. When the entire length of the honeycomb structure
1 in the axial direction is taken as L [mm], L/O is preferably
1.66≦L/O≦7.5, more preferably 2≦L/O≦5. Such
ranges of O and L/O enable to efficiently transfer the heat of the first
fluid to the outer peripheral wall portion which exchanges heat with the
second fluid and to obtain a heat exchanger element capable of reducing
the pressure drop generated by the first fluid while maintaining the
temperature efficiency.

[0046] In a heat exchanger 30 of the present invention, it is preferable
that the first fluid having higher temperature than the second fluid is
passed so that heat is transferred from the first fluid to the second
fluid. When a gas is passed as the first fluid, and a liquid is passed as
the second fluid, heat exchange between the first fluid and the second
fluid can efficiently be performed. That is, a heat exchanger 30 of the
present invention can be applied as a gas/liquid heat exchanger.

[0047] In a heat exchanger 30 of the present invention, by passing the
first fluid having higher temperature than the second fluid through the
cells of the honeycomb structure 1, heat of the first fluid can
efficiently be transferred to the honeycomb structure 1. That is, the
total resistance of heat transfer is the heat resistance from the first
fluid to the honeycomb structure 1+the heat resistance of the partition
walls 4+the heat resistance from the honeycomb structure 1 to the second
fluid, and the rate-determining factor is the heat resistance from the
first fluid to the honeycomb structure 1. In the heat exchanger 30, since
the first fluid passes through the cells 3, the contact area between the
first fluid and the honeycomb structure 1 is large, and the heat
resistance from the first fluid to the honeycomb structure 1, which is
the rate-determining factor, can be reduced. Therefore, in the heat
exchanger element shown in FIG. 1B, even if the length of the honeycomb
structure 1 in the axial direction is made smaller than the
circle-equivalent diameter having the same area as the cross-sectional
area of a cross section in the axial direction, heat exchange can be
performed more sufficiently than ever before.

[0048] Whereas manufacturing of a ceramic heat exchanger of prior art
needs steps of plugging process, slit opening process, and process for
bonding a plurality of formed bodies or fired bodies; the present
invention needs a very small number of steps because, basically,
extrusion can be used as it is. In addition, whereas manufacturing of the
same structure with a heat resistant metal needs steps of pressing
process, welding process, and the like, the present invention does not
need such steps. Therefore, the production costs can be reduced, and
sufficient temperature efficiency can be obtained.

[0049] A heat exchanger 30 of the present invention is constructed of the
honeycomb structure 1 serving as the first fluid passage portion 5 (high
temperature side) of the honeycomb structure, where the first fluid
(heating body) passes, and the casing 21, whose inside serves as the
second fluid passage portion 6. Since the first fluid passage portion 5
is formed of the heat exchanger element of the honeycomb structure 1, the
heat exchange can efficiently be performed. In the honeycomb structure 1,
a plurality of cells 3 functioning as passages by the partition walls 4
are separated and formed, and, for the cell shape, a desired shape may
appropriately be selected from a circle, an ellipse, a triangle, a
quadrangle, other polygons, and the like. Incidentally, when it is
desired to make the heat exchanger 30 large, a module structure, to which
a plurality of honeycomb structures 1 are bonded, can be employed (see
FIG. 4A).

[0050] Though the shape of the honeycomb structure 1 shown in FIGS. 1A and
1B is cylindrical, the shape is not limited to this and may be another
shape such as a quadrangular prism (see FIG. 3A) or a structure of a
honeycomb assembly satisfying the conditions (see FIGS. 4A to 4C).

[0051] The embodiment shown in FIGS. 3A and 3B is a heat exchanger 30
where the first fluid and the second fluid exchange heat by a
countercurrent. The countercurrent means that the second fluid flows in
the reverse direction parallel to the direction of the flow of the first
fluid. The direction of passing the second fluid is not limited to the
opposite direction (countercurrent) of the first fluid-flowing direction
and can appropriately be selected and designed, such as the same
direction (parallel flow) or at a certain angle
(0°<x<180°: excluding a right angle).

[0052] In the heat exchanger 30 shown in FIG. 4A, a plurality of honeycomb
structures 1 are disposed in the casing 21 with the outer peripheral
faces 7 facing one another in the state that the honeycomb structures 1
mutually have a gap where the second fluid passes. Incidentally, FIG. 4A
schematically shows the arrangement of the honeycomb structures 1, where
the casing 21 and the like are omitted. Specifically, the honeycomb
structures 1 are stacked in three rows vertically and four rows
horizontally with gaps. Such a configuration increases the number of
cells 3 where the first fluid passes and can pass a large amount of the
first fluid. In addition, since a plurality of honeycomb structures 1 are
disposed with the outer peripheral faces 7 facing one another in the
state of having gaps, the contact area between the outer peripheral faces
7 of the honeycomb structures 1 and the second fluid is large, and
therefore the heat exchange between the first fluid and the second fluid
can effectively be performed. Incidentally, the circle-equivalent
diameter O is a value obtained regarding each honeycomb structure 1.

[0053] FIGS. 4B and 4C show an embodiment having an equilateral staggered
arrangement of a plurality of honeycomb structures 1. FIG. 4B is a
perspective view, and FIG. 4C is a view from the first fluid inlet port
side. The plural honeycomb structures 1 are disposed in such a manner
that the lines joining the central axes 1j of the honeycomb structures 1
form equilateral triangles. Such arrangement enables to pass the second
fluid uniformly between the honeycomb structures 1 (among the modules),
thereby improving the temperature efficiency. Therefore, in the case of
disposing a plurality of honeycomb structures 1, an equilateral staggered
arrangement is preferable. The equilateral staggered arrangement gives a
kind of a fin structure to make the flow of the second fluid turbulent,
thereby making heat exchange with the first fluid easier.

[0054]FIG. 4D shows an embodiment where honeycomb structures 1 having
different sizes are included. In the embodiment of FIG. 4D, complementary
honeycomb structures 1h are disposed in the gaps among the honeycomb
structures 1 having an equilateral staggered arrangement. The
complementary honeycomb structures 1h are for filling up the gaps, and
the size and shape are different from those of the other general
honeycomb structures 1. That is, it is not necessary that all the
honeycomb structures 1 have the same size and shape. By thus employing
the complementary honeycomb structures lh having different size and
shape, the gaps between the casing 21 and the honeycomb structures 1 are
filled up, thereby improving the temperature efficiency.

[0055] The density of the partition walls 4 of the cells 3 of the
honeycomb structure 1 is preferably 0.5 to 5 g/cm3. When the density
is below 0.5 g/cm3, the partition walls 4 have insufficient
strength, and the partition walls 4 may break due to pressure when the
first fluid passes through the passage. In addition, when it is above 5
g/cm3, the honeycomb structure 1 itself becomes heavy, and the
characteristic of weight reduction may be impaired. The density within
the aforementioned range enables to make the honeycomb structure 1
strong. In addition, an effect of improving thermal conductivity can be
obtained.

[0056] It is preferable to use ceramic excellent in heat resistance for
the honeycomb structure 1, and silicon carbide is particularly preferable
in consideration of heat-transfer performance. However, it is not
necessary that the entire honeycomb structure 1 is constituted of silicon
carbide as long as silicon carbide is contained in the main body. That
is, the honeycomb structure 1 is preferably formed of electrical
conductive ceramic containing silicon carbide. As a physical property of
the honeycomb structure 1, thermal conductivity λ [W/mK] at room
temperature is preferably 10≦λ≦300 though it is not
limited thereto. In place of the electrical conductive ceramic, there can
be used a corrosion resistant metal material such as Fe--Cr--Al-based
alloy.

[0057] In order for a heat exchanger 30 of the present invention to obtain
a high temperature efficiency, it is more preferable to use a material
containing silicon carbide having high thermal conduction as the material
for the honeycomb structure 1. However, since even silicon carbide cannot
obtain high coefficient of thermal conductivity when it is a porous body,
it is more preferable to obtain a dense body structure by impregnating
the porous body with silicon in the production process of the honeycomb
structure 1. By the dense body structure, high coefficient of thermal
conductivity can be obtained. For example, in the case of a silicon
carbide porous body, it is about 20 W/mK. However, by densifying the
body, it can be made about 150 W/mK.

[0058] That is, though Si-impregnated SiC, (Si+Al)-impregnated SiC, metal
composite SiC, Si3N4, and SiC (in particular, densified
material consisting of SiC is preferable), and the like can be employed
as the ceramic material; it is more desirable to employ Si-impregnated
SiC or (Si+Al)-impregnated SiC in order to obtain a dense body structure
for obtaining high temperature efficiency. Since Si-impregnated SiC has a
structure where a solidification of metal silicon melt surrounds the
surface of a SiC particle and where SiC is unitarily bonded by means of
metal silicate, silicon carbide is blocked from an atmosphere containing
oxygen and inhibited from oxidation. Further, though SiC is characterized
by high thermal conductivity and easy heat dissipation, SiC impregnated
with Si is formed densely while showing high thermal conductivity and
heat resistance, thereby showing sufficient strength as a heat transfer
member. That is, a honeycomb structure 1 formed of a Si--SiC based
(Si-impregnated SiC, (Si+Al)-impregnated SiC) material shows a
characteristic excellent in corrosion resistance against acid and alkali
in addition to thermal resistance, thermal shock resistance, and
oxidation resistance and shows high thermal conductivity.

[0059] More specifically, in the case where the honeycomb structure 1
employs Si-impregnated SiC composite material or (Si+Al)-impregnated SiC
as the main component, when the Si content specified by Si/(Si+SiC) is
too small, bonding of adjacent SiC particles by a Si phase becomes
insufficient because of the insufficient bonding material, which not only
lowers thermal conductivity, but also makes it difficult to obtain
strength capable of maintaining a thin wall structure such as a honeycomb
structure. Conversely, when the Si content is too large, it is not
preferable in that negative effects such as lowering of porosity and
reduction in the average pore size are caused in combination by excessive
shrinkage of the honeycomb structure 1 by firing due to the excess
presence of metal silicon than necessary for appropriately bonding the
SiC particles together. Therefore, the Si content is preferably 5 to 50
mass %, more preferably 10 to 40 mass %.

[0060] Such Si-impregnated SiC or (Si+Al)-impregnated SiC has pores filled
up with metal silicon to have a porosity of 0 or nearly 0, is excellent
in oxidation resistance and durability, and is capable of use for a long
period of time under a high temperature atmosphere. Since an oxidation
protective coat is formed when it is once oxidized, oxidation
deterioration is not generated. In addition, since it has high strength
from ordinary temperature to high temperature, a thin and light structure
can be formed. Further, it has high thermal conductivity, which is almost
the same as those of copper and aluminum metals, and high far infrared
radiation emissivity, and it hardly has static electricity because it has
electrical conductivity.

[0061] In the case where the first fluid (high temperature side) passed
through a heat exchanger 30 of the present invention is exhaust gas, it
is preferable that a catalyst is loaded on the partition walls inside the
cells 3 of the honeycomb structure 1 where the first fluid (high
temperature side) passes. It is because it becomes possible to exchange
also reaction heat (exothermic reaction) generated upon exhaust gas
purification in addition to the role of purifying exhaust gas. It is good
to contain at least one kind of an element selected from the group
consisting of noble metals (platinum, rhodium, palladium, ruthenium,
indium, silver, and gold), aluminum, nickel, zirconium, titanium, cerium,
cobalt, manganese, zinc, copper, zinc, tin, iron, niobium, magnesium,
lanthanum, samarium, bismuth, and barium. These may be metals, oxides, or
other compounds. The amount of the catalyst (catalyst metal+carrier)
loaded on the first fluid passage portion 5 of the honeycomb structure 1
where the first fluid (high temperature side) passes is preferably 10 to
400 g/L, and if it is noble metal, more preferably 0.1 to 5 g/L. When the
amount of the catalyst (catalyst metal+carrier) loaded is below 10 g/L,
exhibition of the catalysis may be difficult. On the other hand, when it
is above 400 g/L, production costs may increase in addition to increase
of pressure drop. A catalyst is loaded on the partition walls 4 of the
cells 3 of the honeycomb structure 1 as necessary. In the case of loading
a catalyst, masking is provided on the honeycomb structure 1 so that the
catalyst is loaded on the honeycomb structure 1. After impregnating a
ceramic powder functioning as carrier microparticles with an aqueous
solution containing a catalyst component in advance, catalyst coated
microparticles are obtained by drying and firing. A dispersant (water or
the like) and other additives are added to the catalyst coated
microparticles to prepare coating liquid (slurry), and, after the
partition walls 4 of the honeycomb structure 1 are coated with the
slurry, drying and firing are performed to load a catalyst on the
partition walls 4 of the cells 3 of the honeycomb structure 1.
Incidentally, upon firing, the mask on the honeycomb structure 1 is
removed.

[0062] There is no particular limitation on the heating body as the first
fluid being passed through a heat exchanger 30 of the present invention
having such a configuration as long as it is a medium having heat, such
as gas and liquid. For example, an automobile exhaust gas can be
mentioned as the gas. In addition, there is no particular limitation on
the body to be heated as the second fluid, which receives heat (exchanges
heat) from the heating body, as long as it is a medium having lower
temperature than the heating body, such as gas and liquid. Since at least
one of the partition walls 4 and the outer peripheral wall 7h is formed
densely, liquid is preferably used as the second fluid, and water is
preferable in consideration of handling. However, it is not particularly
limited to water.

[0063] As described above, since the honeycomb structure 1 has high heat
conductivity and a plurality of positions serving as passages by the
partition walls 4, high temperature efficiency can be obtained.
Therefore, the entire honeycomb structure 1 can be downsized, and
therefore it can be mounted on vehicles.

[0064] A further description will be given regarding another embodiment in
the case where the honeycomb structure 1 as the heat exchanger element
has a cylindrical shape. FIG. 5A is a perspective view showing another
embodiment of a heat exchanger 30 where a cylindrical honeycomb structure
1 is housed in a casing 21, FIG. 5B is a cross-sectional view cut along a
cross section parallel to the axial direction, and FIG. 5c is a
cross-sectional view cut along a cross section perpendicular to the axial
direction.

[0065] In the embodiment of FIGS. 5A to 5C, the inlet port 22 and the
outlet port 23 of the second fluid are formed on the same side with
respect to the honeycomb structure 1. According to the installation
location, piping, and the like of the heat exchanger 30, it is possible
to have such a structure of the present embodiment. In the present
embodiment, the second fluid passage portion 6 has an enclosing
structure, wherein it encloses the outer periphery of the honeycomb
structure 1. That is, the second fluid passes so as to enclose the outer
periphery of the honeycomb structure 1.

[0066] FIG. 6 shows a cross-sectional view cut along a cross section
parallel to the axial direction, showing an embodiment of a heat
exchanger 30 where a honeycomb structure 1 is provided with a punching
metal 55 of a hole-provided metal plate having a plurality of holes on
the outer peripheral face 7 thereof in the second fluid passage portion
6. A cylindrical honeycomb structure 1 is housed in the casing 21. The
punching metal 55 is provided so as to engage with the outer peripheral
face 7 of the honeycomb structure 1 in the second fluid passage portion
6. The punching metal 55 is a metal plate subjected to a hole-making
process and is formed into a tubular shape along the shape of the outer
peripheral face 7 of the honeycomb structure 1. That is, since the
punching metal 55 has pores 55a, there are portions where the second
fluid is brought into direct contact with the honeycomb structure 1,
which inhibits reduction of heat transfer. By protecting the honeycomb
structure 1 by covering the outer peripheral face 7 of the honeycomb
structure 1 with the punching metal 55, breakage of the honeycomb
structure 1 can be suppressed. Incidentally, the hole-provided metal
plate means a metal plate having a plurality of holes and is not limited
to the punching metal 55.

[0067] FIGS. 7A and 7B show a heat exchanger 30 of an embodiment where the
casing 21 is formed into a tubular shape and spirally looped around the
honeycomb structure 1 on its outer peripheral face 7. FIG. 7A is a
schematic view for explaining the state where the casing 21 is spirally
looped around the honeycomb structure 1 on its outer peripheral face 7.
FIG. 7B is a schematic view in a direction parallel to the axial
direction, for explaining the state where the casing 21 is spirally
looped around the honeycomb structure 1 on its outer peripheral face 7.
In the present embodiment, since the inside of the tube functions as the
second fluid passage portion 6, and the casing 21 has a shape where it is
looped around the honeycomb structure 1 on its outer peripheral face 7,
the second fluid passing through the second fluid passage portion 6 flows
on the outer peripheral face 7 of the honeycomb structure 1 in a spiral
manner without being brought into direct contact with the outer
peripheral face 7 of the honeycomb structure 1 to exchange heat. Such a
configuration can inhibit leakage and mixing of the first fluid and the
second fluid even if the honeycomb structure 1 has a breakage.

[0068] FIG. 8 shows an embodiment of a heat exchanger 30 where the casing
21 is provided with a tubular portion 21a engaged with the outer
peripheral face 7 of the honeycomb structure 1 and an outside casing
portion 21b forming the second fluid passage portion 6 outside the
tubular portion 21a as a single unit. The tubular portion 21a has a shape
corresponding to the shape of the outer peripheral face 7 of the
honeycomb structure 1, and the outside casing portion 21b has a tubular
shape having a space where the second fluid flows outside the tubular
portion 21a. The inlet port 22 and the outlet port 23 for the second
fluid are formed in a part of the outside casing portion 21b. In the
present embodiment, the second fluid passage portion 6 is formed by being
surrounded by the tubular portion 21a and outside casing portion 21b, and
the second fluid flowing through the second fluid passage portion 6 flows
in the circumferential direction without being brought into direct
contact with the outer peripheral face 7 of the honeycomb structure 1 on
the outer peripheral face 7 of the honeycomb structure 1 to exchange
heat. Such a configuration can inhibit leakage and mixing of the first
fluid and the second fluid even if the honeycomb structure 1 has a
breakage.

[0069] Next, a manufacturing method of a heat exchanger 30 of the present
invention will be described. In the first place, a ceramic forming raw
material is extruded to form a honeycomb formed body having a plurality
of cells 3 partitioned by ceramic partition walls 4, passing through in
the axial direction from one end face 2 to the other end face 2, and
functioning as fluid passages separated and formed therein.

[0070] Specifically, it can be manufactured as follows. After forming a
honeycomb formed body by extruding a kneaded material containing a
ceramic powder into a desired shape, drying and firing are performed to
obtain a honeycomb structure 1 where a plurality of cells 3 functioning
as gas passages are separated and formed by partition walls 4.

[0071] As a material for the honeycomb structure 1, the aforementioned
ceramic materials can be used. For example, in the case of manufacturing
a honeycomb structure having a Si-impregnated SiC composite material as
the main component, in the first place, predetermined amounts of C
powder, SiC powder, binder, and water or an organic solvent are kneaded
together and formed to obtain a formed body having a desired shape. Next,
the formed body is put in a pressure-reduced inert gas or vacuum under a
metal Si atmosphere to impregnate the formed body with metal Si.

[0072] Incidentally, also, in the case of employing Si3N4, SiC,
or the like, the forming raw material is made into a kneaded material,
and extruding the kneaded material in the forming step enables to form a
honeycomb-shaped formed body having a plurality of cells 3 separated by
partition walls 4 and functioning as exhaust gas passages. This is dried
and fired to obtain a honeycomb structure 1. Then, the honeycomb
structure 1 is housed in a casing 21 to manufacture a heat exchanger 30.

[0073] In a heat exchanger 30 of the present invention, the heat exchanger
30 itself can be downsized because it shows high temperature efficiency
in comparison with conventional ones. Further, since it can be
manufactured from a single unitary die by extrusion, costs can be saved.
The heat exchanger 30 can suitably be used in the case where the first
fluid is gas whereas the second fluid is liquid, and can suitably be used
for exhaust heat recovery and the like for improving automobile fuel
consumption, for example.

EXAMPLES

[0074] Hereinbelow, the present invention will be described in more detail
on the basis of Examples. However, the present invention is not limited
to these Examples.

Examples 1 to 15, Comparative Examples 1 to 6

[0075] A heat exchanger 30 having the first fluid passage portion and the
second fluid passage portion formed therein by the honeycomb structure 1
and the casing 21 was manufactured as follows.

[0076] (Manufacturing of Honeycomb Structure)

[0077] After a kneaded material containing a ceramic powder was extruded
into a desired shape, it was dried and fired to manufacture a honeycomb
structure 1 employing silicon carbide as the material and having a main
body size as described in Table 1. Regardless of the external shape of
the honeycomb structure 1, the circle-equivalent diameter O, which is the
diameter of a circle having the same area as the area of the heat
collection portion, was 40 mm, and the entire length L [mm] of the
honeycomb structure 1 in the axial direction was 100 mm. In addition, in
Table 1, there were described thermal conductivity λ [W/Km] of the
material for the partition walls 4, wall thickness t [mm] of the
partition walls 4, and cell density ρ [cell/sq.in.].

[0078] (Casing)

[0079] A stainless steel casing 21 was used as the outside container of
the honeycomb structure 1. In Examples 1 to 15, one honeycomb structure 1
was disposed in the casing 21 (see FIGS. 1A and 2C). The first fluid
passage portion 5 was formed in the honeycomb structure, and the second
fluid passage portion 6 was formed in the casing 21 so as to flow along
the outer periphery of the honeycomb structure 1 (outside structure). In
addition, the casing 21 was provided with pipes for introducing the first
fluid into the honeycomb structure 1 and the second fluid into the casing
21 and for discharging them. Incidentally, the two pathways are
completely separated from each other to avoid the first fluid and the
second fluid from being mixed together (outer periphery flow structure).
The honeycomb structures 1 of Examples 1 to 15 had the same external
shape. In FIG. 2c, the gap L3 between the outer peripheral face 7 of the
honeycomb structure 1 and the inner peripheral face 24 of the casing 21
was 1 mm.

[0080] (First Fluid and Second Fluid)

[0081] The same inlet port temperature and the same flow rate into the
honeycomb structure 1 of the first fluid and the second fluid were
employed. As the first fluid, nitrogen gas (N2) having a temperature
of 500° C. was used. As the second fluid, water was used.

[0082] (Test Method)

[0083] Nitrogen gas was passed through the first fluid passage portion 5
of the honeycomb structure 1, and (cooling) water was passed through the
second fluid passage portion 6 in the casing 21. The flow rate of the
nitrogen gas with respect to the honeycomb structure 1 was 6 L/s. The
flow rate of the (cooling) water was 15 L/min. All the test conditions
such as flow rate of the first fluid and the second fluid were made the
same. Example 1 employed one having the passage for the second fluid in
the outer peripheral portion of the pipe functioning as the first fluid
passage (see FIG. 2B). It was configured so that (cooling) water flowed
outside the pipe (the gap (L3) was 1 mm) (see FIG. 2c). The pipe capacity
of Example 1 means the volume with the first fluid passage. A pressure
gauges were disposed in the first fluid passage pipe in the upstream and
the downstream of the honeycomb structure 1, and pressure drop of the
honeycomb structure 1 was determined.

[0084] (Test Result)

[0085] Table 1 shows temperature efficiency and pressure drop. The
temperature efficiency (%) was calculated by the formula 1 by calculating
the ΔT° C. (outlet port temperature-inlet port temperature
of the honeycomb structure 1) of each of the first fluid (nitrogen gas)
and the second fluid (water). (Formula 1) Temperature efficiency
(%)=(inlet port temperature of the first fluid (gas)-outlet port
temperature of the second fluid (cooling water))/(inlet port temperature
of the first fluid (gas)-outlet port temperature of the first fluid
(gas))×100

[0086] Table 1 shows the temperature efficiency and pressure drop when the
cell structure (thickness t of the partition walls 4 of the cells, and
cell density ρ) was changed while the entire honeycomb length (L=100
mm) of the heat collection portion and thermal conductivity (100 [W/Km])
of the material for the partition walls 4 of the honeycomb were made up
the same number. At this time, by satisfying both a pressure drop of
below 5.0 [kPa] and a temperature efficiency of above 50%, there can be
achieved a weight-reduced and simple structure in comparison with a
conventional product. The pressure drop becomes larger as the partition
walls of the cells and the cell density increases, and the pressure drop
exceeds 5.0 [kPa] when the wall thickness is 0.3 with a cell density of
600. On the other hand, when the wall thickness is 0.1 with a cell
density of 100, the temperature efficiency does not exceed 50%.

Examples 16 to 23, Comparative Examples 7 to 9

[0087] Next, honeycomb structures were manufactured by varying thermal
conductivity of the material of the partition walls 4 with the same
external shape (circle-equivalent diameter O of 45 mm and entire length L
of 100 mm) of the honeycomb structure 1 and the same wall thickness t of
the partition walls 4. The results are shown in Table 2.

[0088] Though the temperature efficiency is low when the cell density is
100, it tends to become larger as the coefficient of thermal conductivity
of the partition walls and the cell density increase. In order to satisfy
the requirements of a heat exchanger element having better performance
than a conventional one, specifically, a pressure drop of below 5.0 [kPa]
and a temperature efficiency of above 50%; from Tables 1 and 2, it is
necessary to satisfy all of t≧0.2, ρ≧100,
20≦t×ρ≦250, and 10,000≦λ×ρ
when the coefficient of thermal conductivity of the partition walls of
the honeycomb structure is taken as λ [W/Km], the wall thickness of
the partition walls is taken as t [mm], and the cell density is taken as
ρ [cells/sq.in.].

Examples 24 to 34

[0089] Next, thermal conductivity of the partition walls of the honeycomb
structure 1 was determined as λ [W/Km], the wall thickness of the
partition walls was determined as t [mm], and the cell density was
determined as ρ [cells/sq.in.]. Honeycomb structures 1 where the
outer diameter (circle-equivalent diameter O) and the entire length (L)
were changed with employing the same thermal conductivity, wall
thickness, and the cell density. The results are shown in Table 3.

[0090] The temperature efficiency has a tendency to rise as the outer
diameter (circle-equivalent diameter O) increases and fall after it
reaches a peak whereas the pressure drop has a tendency to decrease. In
order to satisfy the aforementioned volume, pressure drop, and
temperature efficiency, it is necessary to satisfy all of
20≦O≦60, and 1.66≦L/O≦7.5.

INDUSTRIAL APPLICABILITY

[0091] There is no restriction as to the use as far as the heat exchanger
of the present invention is used for the heat exchange purpose between a
heating body (high temperature side) and a body to be heated (low
temperature side) even in the automobile fields and industrial fields. In
the case where it is used for exhaust heat recovery from exhaust gas in
the automobile fields, it can be used to improve fuel consumption of an
automobile.